White-emitting monomolecular compound using excited-state intramolecular proton transfer, organic electroluminescent element and laser device using the same

ABSTRACT

Provided are a white-emitting monomolecular compound using excited-state intramolecular proton transfer (ESIPT) characteristics, and an organic electroluminescence device and a laser device comprising same. The white-emitting monomolecular compound according to the present invention is prepared by covalently bonding at least two types of molecules which produce different colors and have excited-state intramolecular proton transfer (ESIPT) characteristics. The white-emitting monomolecular compound according to the present invention achieves white luminescence irrespective of the concentration thereof and of the state of the materials thereof, and therefore can be used in a variety of fields including an organic electroluminescence device and a laser device.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a divisional, and claims the benefit, of U.S. patentapplication Ser. No. 13/264,968, now U.S. Pat. No. 8,569,510, entitledWHITE-EMITTING COMPOUNDS USING EXCITED-STATE INTRAMOLECULAR PROTONTRANSFER, ORGANIC ELCTROLUMINESCENT ELEMENT AND LASER MATERIAL USING THESAME, and filed Oct. 17, 2011 (the “'968 Application”) which claimspriority to PCT/KR2010/002482 filed Apr. 21, 2010 which claims priorityto and the benefit of Korean Patent Application No. 10-2009-0034806,filed on Apr. 21, 2009, and Korean Patent Application No.10-2010-0035707, filed on Apr. 19, 2010. All of the aforementionedapplications are incorporated herein in their respective entireties bythis reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

Aspects of the present invention relate to a white-emittingmonomolecular compound using excited-state intramolecular protontransfer (ESIPT), an organic electroluminescent element and a laserdevice using the same. More particularly, aspects of the presentinvention relate to a white-emitting monomolecular compound using ESIPT,which are prepared by synthesizing at least two types of compoundshaving ESIPT characteristics in an intramolecular state, an organicelectroluminescent element and a laser device using the same.

2. Description of the Related Art

In recent years, studies for developing efficient light-emittingmonomolecular compounds for a next generation flat display or whiteillumination light source are actively in progress. In particular, sincewhite-emitting monomolecular compounds have various advantages,including improved stability, excellent reproducibility, and easefabrication of devices, compared to a white luminescence system usingpolymeric materials or various molecular compounds, development of thewhite-emitting monomolecular compounds has become important more andmore.

White luminescence over the entire visible area ranging from about 400to 700 nm is generally achieved by combining two or more kinds offluorescent or phosphorescent materials having different emissionranges.

Devices emitting substantially white light by combining two or morekinds of fluorescent or phosphorescent materials are disclosed in KoreanPatent Publication No. 2003-0015870 by Eastman Kodak Company, KoreanPatent Publication No. 2004-0082286 by Semiconductor Energy LaboratoryK.K. of Japan, and Korean Patent Publication No. 2004-0100523 by BistormCo., Ltd. White-emitting monomolecular compounds which have beenreported to date include “White luminescence from an assembly comprisingluminescent iridium and europium complexes” by Coppo P. et al., Angew.Chem. Int. Ed. 46 (12), 1806-1810 (2005), and “An organic white-lightemitting fluorophore” by Yang, Y., Lowry, M., Schowalter, C. M.,Fakayode, S. O., J. Am. Chem. Soc. 128, 14081-14092 (2006).

Most of the above-referenced methods utilize partial energy transferbetween a higher energy band gap donor and a lower energy band gapacceptor.

According to the known methods, however, color control is quitedifficult to achieve simply by mixing even a small amount of an emissivedopant with a host since light emission is easily affected by a dopanthaving a small band gap. This problem arises from the inter-dopantFörster-type energy transfer between the higher band gap donor and theclosely located lower band gap acceptor by means of spectral matching.In addition, the energy transfer characteristics are considerablyaffected by the concentration and state of emitting material. Thus, ifthe concentration and state of the emitting material vary, color purityand stability may considerably deteriorate.

For these reasons, it has been considered that development ofwhite-light emitting compounds is quite difficult to achieve,irrespective of the concentration or state of material.

The inventors of the present invention published a paper reporting thatthe use of molecules having excited-state intramolecular proton transfer(ESIPT) characteristic may restrict energy transfer between differentchromophores: Sehoon Kim, Jangwon Seo, Ho Kuk Jung, Jang-Joo Kim, andSoo Young Park, “White Luminescence from Polymer Thin Films ContainingExcited-State Intramolecular Proton Transfer (ESIPT) Dyes”, Adv. Mater.,17, 2077-2082, (2005) In the report, the inventors disclosed that awhite luminescence organic electroluminescent element could be easilyfabricated when ESIPT molecules having different fluorescent colors aredispersed in a monomolecular polymer.

However, since a monomolecular white emitter is not used in the methoddisclosed in the paper published by the present inventors, there is aproblem with reproducibility of white luminescence. To solve theproblem, the present inventors conducted intensive researches anddiscovered that the interaction between energy acceptor and donor can becompletely restricted by appropriately designing and synthesizing ESIPTmolecules, thereby implementing efficient white luminescence in amonomolecular state. That is to say, the present inventors developedmonomolecular compounds capable of emitting white light covering theentire visible area, irrespective of the concentration and state of thecompound, by newly designing and synthesizing imidazole and oxadiazolecyclic molecules containing hydroxyphenyl and hydroxynaphthyl groups ofspecific structures having ESIPT characteristics, thereby completing thepresent invention.

BRIEF SUMMARY OF THE INVENTION

Aspects of the present invention provide a white-emitting monomolecularcompound capable of emitting white light using molecules having ESIPTcharacteristics.

Other aspects of the present invention provide an organicelectroluminescent element including the white-emitting monomolecularcompound.

Aspects of the present invention further provide a laser deviceincluding the white-emitting monomolecular compound.

In accordance with one aspect of the present invention, there isprovided a white-emitting monomolecular compound using excited-stateintramolecular proton transfer (ESIPT) characteristics, produced bycovalently bonding at least two types of ESIPT molecules developingdifferent colors.

In accordance with another aspect of the present invention, there isprovided an organic electroluminescent element comprising thewhite-emitting monomolecular compound.

In accordance with still another aspect of the present invention, thereis provided a laser device including the white-emitting monomolecularcompound.

As described above, according to the present invention, white-emittingmonomolecular compounds are provided by covalently bonding at least twotypes of ESIPT molecules. Thus, compared to the conventional whiteluminescence technology using a combination of two or more molecules,the luminescence monomolecular compounds according to the presentinvention have superior reproducibility and demonstrate stability,enhanced life characteristic, excellent quantum efficiency and a widevariety of applications irrespective of the concentration of thematerial or the state of the material in either a solid or liquid state.

In particular, when the white-emitting monomolecular compounds accordingto the present invention are used as emissive materials for an organicelectroluminescent element, they have advantages, including costreduction and simplifying of fabrication process. Additionally, thewhite-emitting monomolecular compounds according to the presentinvention may be used in various applications including organicelectroluminescent elements, laser devices, UV stabilizers,chemosensors, solar concentrators, and so on.

Additional aspects and/or advantages of the invention will be set forthin part in the description which follows and, in part, will be obviousfrom the description, or may be learned by practice of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The objects, features and advantages of the present invention will bemore apparent from the following detailed description in conjunctionwith the accompanying drawings, in which:

FIG. 1 is a schematic representation of the principle of colordevelopment in molecules having ESIPT characteristics;

FIG. 2 illustrates the complementary color relationship in CIE 1931coordinates;

FIG. 3 is a schematic representation of the principle of whiteluminescence using ESIPT;

FIG. 4 illustrates photoluminescence (PL) spectral analysis results ofwhite-emitting monomolecular compounds according to the presentinvention;

FIG. 5 illustrates photoluminescence (PL) spectral analysis results ofconventional ESIPT monomolecular as measured in Example 1;

FIG. 6 illustrates CIE color coordinates of a white-emittingmonomolecular compound according to the present invention and theconventional ESIPT monomolecules, as measured in Example 1;

FIG. 7 illustrates emission intensity depending on the change in theconcentration of a white-emitting monomolecular compound in Example 2 ofthe present invention;

FIG. 8 illustrates UV lamp irradiation results for white-emittingmonomolecular a compounds in Example 3;

FIGS. 9 and 10 illustrate normalized intensities of a white-emittingmonomolecular compound having Formula 18 in Example 4 of the presentinvention over time (ps) in 450 nm and 690 nm, respectively;

FIGS. 11 and 12 illustrate the intensity normalized per unit time of aconventional ESIPT monomolecular compound, as measured in Example 4;

FIG. 13 illustrates the EL spectrum of an organic electroluminescentelement fabricated using a white-emitting monomolecular compound havingFormula 18 prepared in Experimental Example 1 of the present invention;and

FIG. 14 illustrates the PL intensity dependent EL spectral changes of awhite-emitting monomolecular compound having Formula 18 prepared inExperimental Example 2.

DETAILED DESCRIPTION OF THE INVENTION

Hereinafter, embodiments of the present invention will be described indetail with reference to the accompanying drawings.

The present invention provides a white-emitting monomolecular compoundhaving at least two kinds of molecules having excited-stateintramolecular proton transfer (ESIPT) characteristics covalently bondedto provide different colors.

The ESIPT is a phototautomerization in which protons are transferred inthe excited states of molecules, as shown in FIG. 1. That is to say, themolecule having ESIPT having characteristics, a proton donor such as—OH, —NH, or —SH group having an intramolecular hydrogen bond and aproton acceptor such as N, O, S, or F, exists stably in the enol formwhen it is in the ground state and in the keto form when it is in theexcited state. Thus, the ESIPT molecule usually emits light in the ketoform generated after undergoing proton transfer in the excited statewithin a very short time (in picosecond (ps) level). Accordingly, themolecule having ESIPT having characteristics (to be briefly referred toas “ESIPT molecule”) has a four-level energy structure, as shown inFIG. 1. In addition, Stokes' shift between absorption and emissionenergy is maximized by above-described mechanisim, thereby minimizing areduction in fluorescence due to partial overlap between absorption andluminescence. In addition, population inversion is facilitated due tofour-level photophysical properties. Further, stimulated emission can beadvantageously realized due to a high optical gain.

The white-emitting monomolecular compound according to the presentinvention may have a structure represented by Formula 1 or Formula 2:

wherein A and B are ESIPT molecules emitting different colors,respectively, R₁ and R₂ are functional groups having a proton donor anda proton acceptor capable of forming an intramolecular hydrogen bond,and Y indicates a covalent bond between the ESIPT molecules:

wherein A, B and C are ESIPT molecules emitting different colors,respectively; R₁ and R₂ are functional groups having a proton donor anda proton acceptor capable of forming an intramolecular hydrogen bond,and Y₁ and Y₂, which may be the same or different, indicate a covalentbonds between the ESIPT molecules.

In the white-emitting monomolecular compound having Formula 1, A and Brepresent ESIPT molecules developing different colors, respectively,preferably ESIPT molecules developing complementary colors to achievewhite luminescence by combining the colors.

Here, the complementary colors refer to paired colors, such as A-B, C-D,and E-F, as shown in FIG. 2, which are symmetrically positioned withrespect to ideal white light (x,y)=(0.33, 0.33) on the color coordinateslike CIE 1931 coordinates. White light can be generated by summing threeprimary colors (red, green and blue) of light. Thus, the white-emittingmonomolecular compound having Formula 2 may also be achieved. That is tosay, the white-emitting monomolecular compound according to the presentinvention may also achieve white luminescence in the form of amonomolecular compound prepared by covalently bonding three ESIPTmolecules developing different colors.

In order to achieve white luminescence using a monomolecular compound bycovalently bonding at least two types of molecules developing differentcolors, like in the present invention, it is necessary to use a systemwithout energy transfer. In the present invention, the energy transfercan be prevented by completely restricting an interaction between anenergy acceptor and an energy donor using ESIPT characteristics, therebyachieving efficient white luminescence using a monomolecular compound,which will be described in more detail with reference to FIG. 3.

The white-emitting monomolecular compound according to the presentinvention is capable of preventing energy transfer due to four-levelenergy structures of the respective ESIPT molecules covalently bondedwith each other. That is to say, as shown in FIG. 3, absorbance of anorange luminescent phosphor and absorbance of a blue luminescentphosphor occur in the same UV area. Thus, since the emission energy ofthe blue luminescent phosphor is not spectrally overlapped with theabsorption energy of the orange luminescent phosphor,absorption-emission energy transfer or Förster resonance energy transferdoes not occur.

Basically, the energy transfer occurs by an interaction between theexcited state (K₁*, K₂* of FIG. 3) of an energy donor and the groundstate (K₁ and K₂) of an energy acceptor. However, in the whiteluminescent material based on ESIPT, like in the present invention,since the ground states (K₁, K₂) of the keto energy acceptor haveunstable energy, they are transferred within a very short time to groundstates (E₁ and E₂), respectively. Thus, there is no population of theground states (K₁ and K₂). Therefore, the interaction between theexcited state of the energy donor and the ground state of the energyacceptor can be fundamentally prevented.

Consequently, when ESIPT molecules are bonded to each other, energytransfer can be completely prevented, irrespective of the concentrationsand states of materials, thereby achieving novel, efficientwhite-emitting monomolecular compounds.

The ESIPT molecules employed in Formulae 1 and 2 may include well knowncompounds. Preferably, the ESIPT molecules employed in Formulae 1 and 2may include compounds represented by Formulae 3 to 7:

wherein R₁ to R₄ are each independently selected from the groupconsisting of a hydrogen atom, a hydroxy group, a linear, branched orcyclic C1-C20 alkyl group, a C1-C20 alkoxy group, a substituted orunsubstituted C1-C20 carbonyl group, an aryloxy group substituted withan aromatic or cyclic compound, a halogen atom, a trifluoromethyl group,a C1-C20 sulfonic group substituted with an alkyl group, a sulfonicgroup substituted with an aromatic cyclic compound or an aryl group, aC1-C20 substituted alkylamide group, an arylamide group substituted withan aromatic cyclic compound or an aryl group, an amino group, a nitrogroup, and a cyano group; and at least one of R₁ and R₂ is selected fromthe group consisting of a hydroxyl group, an amino group, an alkylamidegroup, an arylamide group, a sulfone amide group, a sulfonic groupsubstituted with an aromatic cyclic compound or an aryl group, a thiolgroup, and a fluorous acid group, which contain hydrogen capable offorming a hydrogen bond with a nitrogen atom of an adjacent ring;

wherein R₁ is selected from the group consisting of a hydroxyl group, anamino group, an alkylamide group, an arylamide group, a sulfone amidegroup, a sulfonic group substituted with an aromatic cyclic compound oran aryl group, a thiol group, and a fluorous acid group, which containhydrogen capable of forming a hydrogen bond with a nitrogen atom of anadjacent ring; and R₂ to R₅ are each independently selected from thegroup consisting of a hydrogen atom, a hydroxy group, a linear, branchedor cyclic C1-C20 alkyl group, a C1-C20 alkoxy group, a substituted orunsubstituted C1-C20 carbonyl group, an aryloxy group substituted withan aromatic or cyclic compound, a halogen atom, a trifluoromethyl group,a C1-C20 sulfonic group substituted with an alkyl group, a sulfonicgroup substituted with an aromatic cyclic compound or an aryl group, aC1-C20 substituted alkylamide group, an arylamide group substituted withan aromatic cyclic compound or an aryl group, an amino group, a nitrogroup, and a cyano group;

wherein R₁ is selected from the group consisting of a hydroxyl group, anamino group, an alkylamide group, an arylamide group, a sulfone amidegroup, a sulfonic group substituted with an aromatic cyclic compound oran aryl group, a thiol group, and a fluorous acid group, which containhydrogen capable of forming a hydrogen bond with a nitrogen atom of anadjacent ring; and R₂ to R₄ are each independently selected from thegroup consisting of a hydrogen atom, a hydroxy group, a linear, branchedor cyclic C1-C20 alkyl group, a C1-C20 alkoxy group, a substituted orunsubstituted C1-C20 carbonyl group, an aryloxy group substituted withan aromatic or cyclic compound, a halogen atom, a trifluoromethyl group,a C1-C20 sulfonic group substituted with an alkyl group, a sulfonicgroup substituted with an aromatic cyclic compound or an aryl group, aC1-C20 substituted alkylamide group, an arylamide group substituted withan aromatic cyclic compound or an aryl group, an amino group, a nitrogroup, and a cyano group;

wherein R₁ is selected from the group consisting of a hydroxyl group, anamino group, an alkylamide group, an arylamide group, a sulfone amidegroup, a sulfonic group substituted with an aromatic cyclic compound oran aryl group, a thiol group, and a fluorous acid group, which containhydrogen capable of forming a hydrogen bond with a nitrogen atom of anadjacent ring; and R₂ to R₅ are each independently selected from thegroup consisting of a hydrogen atom, a hydroxy group, a linear, branchedor cyclic C1-C20 alkyl group, a C1-C20 alkoxy group, a substituted orunsubstituted C1-C20 carbonyl group, an aryloxy group substituted withan aromatic or cyclic compound, a halogen atom, a trifluoromethyl group,a C1-C20 sulfonic group substituted with an alkyl group, a sulfonicgroup substituted with an aromatic cyclic compound or an aryl group, aC1-C20 substituted alkylamide group, an arylamide group substituted withan aromatic cyclic compound or an aryl group, an amino group, a nitrogroup, and a cyano group; and

wherein R₁ is selected from the group consisting of a hydroxyl group, anamino group, an alkylamide group, an arylamide group, a sulfone amidegroup, a sulfonic group substituted with an aromatic cyclic compound oran aryl group, a thiol group, and a fluorous acid group, which containhydrogen capable of forming a hydrogen bond with a nitrogen atom of anadjacent ring; and R₂ to R₅ are each independently selected from thegroup consisting of a hydrogen atom, a hydroxy group, a linear, branchedor cyclic C1-C20 alkyl group, a C1-C20 alkoxy group, a substituted orunsubstituted C1-C20 carbonyl group, an aryloxy group substituted withan aromatic cyclic compound or an aryl group, a halogen atom, atrifluoromethyl group, a C1-C20 sulfonic group substituted with an alkylgroup, a sulfonic group substituted with an aromatic cyclic compound oran aryl group, a C1-C20 substituted alkylamide group, an arylamide groupsubstituted with an aromatic cyclic compound or an aryl group, an aminogroup, a nitro group, and a cyano group.

In the white-emitting monomolecular compound according to the presentinvention, the ESIPT molecules developing different colors are linked toeach other by covalent bonds. Here, the covalent bonds between the ESIPTmolecules may have various structures defined by Formulae 8 to 16:

That is to say, the white-emitting monomolecular compound according tothe present invention is a compound having at least two types of ESIPTmolecules developing different colors, connected to each other asrepresented by Formulae 8 to 16, the at least two types of ESIPTmolecules rendering white light by combining colors developed by theESIPT molecules of Formulae 3 to 7.

Specific examples of the white-emitting monomolecular compound accordingto the present invention include the followings.

First, the white-emitting monomolecular compound represented by Formula1 is preferably a compound of Formula 17:

wherein R₁ and R₂ are each independently selected from the groupconsisting of a hydroxyl group, an amino group, an alkylamide group, anarylamide group, a sulfone amide group, a sulfonic group substitutedwith an aromatic cyclic compound or an aryl group, a thiol group, and afluorous acid group, which contain hydrogen capable of forming ahydrogen bond with a nitrogen atom of an adjacent ring.

More preferably, the compound of Formula 17 is a compound of Formula 18:

In addition, the white-emitting monomolecular compound represented byFormula 1 is preferably a compound of Formula 19:

wherein R₁ and R₂ are each independently selected from the groupconsisting of a hydroxyl group, an amino group, an alkylamide group, anarylamide group, a sulfone amide group, a sulfonic group substitutedwith an aromatic cyclic compound or an aryl group, a thiol group, and afluorous acid group, which contain hydrogen capable of forming ahydrogen bond with a nitrogen atom of an adjacent ring.

More preferably, the compound of Formula 19 is a compound of Formula 20:

The white-emitting monomolecular compound represented by Formula 1 ispreferably a compound of Formula 21:

wherein R₂ to R₄ are each independently selected from the groupconsisting of a hydrogen atom, a hydroxy group, a linear, branched orcyclic C1-C20 alkyl group, a C1-C20 alkoxy group, a substituted orunsubstituted C1-C20 carbonyl group, an aryloxy group substituted withan aromatic or cyclic compound, a halogen atom, a trifluoromethyl group,a C1-C20 sulfonic group substituted with an alkyl group, a sulfonicgroup substituted with an aromatic cyclic compound or an aryl group, aC1-C20 substituted alkylamide group, an arylamide group substituted withan aromatic cyclic compound or an aryl group, an amino group, a nitrogroup, and a cyano group; and at least one of R₁ and R₂ or R₃ isselected from the group consisting of a hydroxyl group, an amino group,an alkylamide group, an arylamide group, a sulfone amide group, asulfonic group substituted with an aromatic cyclic compound or an arylgroup, a thiol group, and a fluorous acid group, which contain hydrogencapable of forming a hydrogen bond with a nitrogen atom of an adjacentring.

The compound of Formula 21 is preferably a compound of Formula 22:

In addition, the white-emitting monomolecular compound represented byFormula 2 is preferably a compound of Formula 23:

wherein R₂ and R₃ are each independently selected from the groupconsisting of a hydrogen atom, a hydroxy group, a linear, branched orcyclic C1-C20 alkyl group, a C1-C20 alkoxy group, a substituted orunsubstituted C1-C20 carbonyl group, an aryloxy group substituted withan aromatic or cyclic compound, a halogen atom, a trifluoromethyl group,a C1-C20 sulfonic group substituted with an alkyl group, a sulfonicgroup substituted with an aromatic cyclic compound or an aryl group, aC1-C20 substituted alkylamide group, an arylamide group substituted withan aromatic cyclic compound or an aryl group, an amino group, a nitrogroup, and a cyano group; and at least one of R₁, R₂ and R₃ is selectedfrom the group consisting of a hydroxyl group, an amino group, analkylamide group, an arylamide group, a sulfone amide group, a sulfonicgroup substituted with an aromatic cyclic compound or an aryl group, athiol group, and a fluorous acid group, which contain hydrogen capableof forming a hydrogen bond with a nitrogen atom of an adjacent ring.

More preferably, the compound of Formula 23 is a compound of Formula 24:

The white-emitting monomolecular compounds according to the presentinvention, as represented by Formulae 1 and 2, in particular, imidazoleand oxadiazole cyclic compounds, are capable of achieving whiteluminescence while having high stability, excellent quantum efficiency,extended emissive life time characteristics, and high thermal stability.

The white-emitting monomolecular compounds can be applied to a varietyof fields. For example, an emissive layer can be formed by depositingonly the white-emitting monomolecular compound according to the presentinvention or dispersing the white-emitting monomolecular compoundaccording to the present invention in a host material, to be used infabricating an organic electroluminescent element. Further, thewhite-emitting monomolecular compounds according to the presentinvention may be used in various applications including organicelectroluminescent elements, laser devices, UV stabilizers,chemosensors, solar concentrators, and so on.

Hereinafter, the organic electroluminescent element including thewhite-emitting monomolecular compound according to the present inventionwill be described in more detail. However, the use of the white-emittingmonomolecular compounds according to the present invention is notlimited to the organic electroluminescent element described below.

The white-emitting monomolecular compound according to the presentinvention may be used as an emissive material or a dopant.

Here, the organic electroluminescent element may have a structure thatis known well in the art. For example, the organic electroluminescentelement may include a positive electrode, a hole injecting layer, a holetransporting layer, an emissive layer, an electron injecting layer, anelectron transporting layer, and a negative electrode, stacked on asubstrate.

The white-emitting monomolecular compound according to the presentinvention may be included in one selected from the group consisting ofthe hole injecting layer, the hole transporting layer, the emissivelayer, the electron injecting layer, and the electron transportinglayer. Preferably, the white-emitting monomolecular compound accordingto the present invention may be included in the emissive layer.

The positive electrode may be formed of, for example, a metal oxide or ametal nitride, such as ITO, IZO, zinc oxide, zinc aluminum oxide ortitanium nitride; a metal such as gold, platinum, silver, copper,aluminum, nickel, cobalt, lead, molybdenum, tungsten, tantalum orniobium; alloys of these metals or alloys of copper iodides; or aconductive polymer such as polyaniline, polythiophene, polypyrrole,polyphenylenevinylene, or poly(3-methylthiophene). The positiveelectrode may be formed of at least one selected from the above-listedmaterials, either alone or in mixtures of two or more materials. Inaddition, the positive electrode may have a multi-layered structurehaving multiple layers having the same composition or differentcompositions.

Known materials may be used as the hole injecting layer and the holeinjecting layer may be formed of a material to a thickness of 5 nm-100nm, the material including, but not limited to, PEDOT/PSS or copperphthalocyanine (CuPc),4,4′,4″-tris(3-methylphenylphenylamino)triphenylamine(m-MTDATA), and4,4′,4″-tris((N-(naphthalene-2-yl)-N-phenylamino)triphenylamine(2-TNATA).

Known materials may be used as the hole transporting layer andnon-limiting examples of the hole transporting layer may include4,4′-bis[N-(1-naphthyl)-N-phenyl-amino]-biphenyl (NPD), andN,N′-diphenyl-N,N′-bis(3-methylphenyl)-1,1′-biphenyl-4,4′-diamine (TPD).

As described above, the emissive layer preferably includes thewhite-emitting monomolecular compound according to the presentinvention. That is to say, the emissive layer may be formed bydepositing one selected from the white-emitting monomolecular compoundsaccording to the present invention or depositing together at least twotypes of the white-emitting monomolecular compounds according to thepresent invention. When necessary, the emissive layer may be formed bydispersing at least one selected from the white-emitting monomolecularcompounds according to the present invention in a host material.Alternatively, a dopant material may be additionally used in forming theemissive layer.

Non-limiting examples of the host material may include(4,4′-bis(2,2-diphenyl-ethene-1-yl)diphenyl (DPVBi), bis(styryl)amines(DSA),bis(2-methyl-8-quinolinolato)(triphenylsiloxy)aluminum(III)(SAlq),bis(2-methyl-8-quinolinolato)(para-phenolato)aluminum (III) (BAlq),bis(salen) zinc (II),1,3-bis[4-(N,N-dimethylamino)phenyl-1,3,4-oxadiazolyl]benzene(OXD8),3-(biphenyl-4-yl)-5-(4-dimethylamino)-4-(4-ethylphenyl)-1,2,4-triazole(p-EtTAZ),3-(4-biphenyl)-4-phenyl-5-(4-tertiary-butylphenyl)-1,2,4-triazole(TAZ),2,2′,7,7′-tetrakis(biphenyl-4-yl)-9,9′-spirofluorene (Spiro-DPVBI),tris(para-tertiary-phenyl-4-yl)amine(p-TTA),5,5-bis(dimethylboryl)-2,2-bithiophene (BMB-2T) and perylene.

In addition, usable examples of host or dopant materials may includetris(8-quinolato)aluminum (III) (Alq3),DCM1(4-dicyanomethylene-2-methyl-6-(para-dimethylaminostyryl)-4H-pyran),DCM2(4-dicyanomethylene-2-methyl-6-(zulolidine-4-yl-vinyl)-4H-pyran),DCJT(4-(dicyanomethylene)-2-methyl-6-(1,1,7,7-tetramethylzulolidyl-9-enyl)-4H-pyran),DCJTB(4-(dicyanomethylene)-2-tertiarybutyl-6-(1,1,7,7-tetramethylzulolidyl-9-enyl)-4H-pyran),DCJTI(4-dicyanomethylene)-2-isopropyl-6-(1,1,7,7-tetramethylzulolidyl-9-enyl)-4H-pyran),Nile red, and Rubrene.

The electron transporting layer materials are known in the related artand examples of materials that may be suitable for the electrontransporting layer may include aryl-substituted oxadiazole,aryl-substituted triazole, aryl-substituted phenanthroline, benzoxazole,and benzothiazole compounds.

Specific examples of the electron transporting layer compound mayinclude 1,3-bis(N,N-t-butyl-phenyl)-1,3,4-oxadiazole(OXD-7),3-phenyl-4-(1′-naphthyl)-5-phenyl-1,2,4-triazole (TAZ),2,9-dimethyl-4,7-diphenyl-phenanthroline (“BCP”),bis(2-(2-hydroxyphenyl)-benzoxazolate)zinc, andbis(2-(2-hydroxyphenyl)-benzothiazolate)zinc. Other electrontransporting layer materials may include(4-biphenyl)(4-t-butylphenyl)oxidiazole (PDB), and tris(8-quinolato)aluminum (III) (Alq3).

Known materials may be used as materials of the electron injecting layerand the negative electrode. For example, LiF may be used as the electroninjecting layer, but not limited thereto, and a metal having a low workfunction, such as Al, Ca, Mg, or Ag, may be used as a material of thenegative electrode. Aluminum (Al) is preferably used as the material ofthe negative electrode.

The organic electroluminescent element according to the presentinvention may be applied to various kinds of display devices. Forexample, the organic electroluminescent element may be used as a lightsource of a backlight unit, or an independent light source. The displaydevices may be ones using a backlight unit, for example, an organiclight-emitting diode (OLED).

Hereinafter, a laser device using the white-emitting monomolecularcompound according to the present invention will be described in moredetail. However, the use of the white-emitting monomolecular compoundaccording to the present invention is not limited to the laser devicedescribed below.

In general, ESIPT molecules have their own four-level systems. Inparticular, the ESIPT molecules easily undergo population inversion whenthey exist in keto forms. Thus, the ESIPT molecules have a high opticalgain due to pumping using laser. Therefore, the white-emittingmonomolecular compound according to the present invention may also beuseful for the laser device.

For example, the compound of Formula 18 is allowed to grow into a singlecrystalline material in the presence of ethylacetate, followed bypumping using a 355 nm Nd:YAG laser. Here, pulse-excited emissionspectra were measured by using an actively/passively mode-locked Nd:YAGLaser (Quantel, YG701). As a result, amplified spontaneous emission(ASE), also known as mirrorless lasing, was easily observed.

The present invention will now be described in greater detail withreference to the following examples. The following examples are forillustrative purposes only and are not intended to limit the scope ofthe invention.

SYNTHESIS EXAMPLE

In order to efficiently cover the visible light area ranging from 400 nmto 700 nm, 2-(1,4,5-triphenyl-1H-imidazole-2-yl)phenol (HPI, λ_(max)=460nm),2,5-bis(5-(4-tert-butylphenyl)-1,3,4-oxadiazole-2-yl)benzene-1,4-diol(DOX, λ_(max)=580 nm),3-(1,4,5-triphenyl-1H-imidazole-2-yl)naphthalene-2-ol (HPNI, λ_(max)=580nm) were selected from ESIPT molecules having emission wavelengths ofcomplementary colors for blue and orange, and the white-emittingmonomolecular compounds of Formulae 18, 20, 22 and 24, including theselected molecules or combinations thereof, were synthesized.

Synthesis Example 1 3-(4-nitrophenoxy)benzoic acid

7.52 ml of fluoro-4-nitrobenzene (70.8 mmol) and 9.79 g of3-hydroxybenzoic acid (70.8 mmol) were dissolved in 150 ml of DMSO atroom temperature, 21 g of potassium carbonate (151.9 mmol) was addedthereto, heated to 130° C., and then reacted for 12 hours. The reactantsolution was poured into excess water, neutralized with hydrochloricacid, filtered, and dried to yield a product having Formula 25 as awhite powder (18.7 g, Yield 98%). ¹H NMR (300 MHz, CDCl₃) analyticalresults of the product were as follows:

¹H NMR (300 MHz, CDCl₃):□ [ppm] 7.03 (d, 2H), 7.33 (d, 1H), 7.54 (t,1H), 7.80 (s, 1H), 7.98 (d, 1H), 8.22 (d, 2H), 12.70 (s, 1H)

Synthesis Example 2 ethyl3-(4-nitrophenoxy)benzoate

18 g of 3-(4-nitrophenoxy)benzoic acid (69.4 mmol) prepared in SynthesisExample 1 was dissolved in 120 ml of ethanol, 35 ml of hydrochloric acid(10N) was added thereto, heated to 110° C. and then reacted for 12hours. The reactant solution was poured into excess water, neutralizedwith a 1N aqueous solution of sodium chloride, filtered, and dried withmagnesium sulfate, followed by removing ethylacetate, to yield a tackyproduct having Formula 26 (19 g (˜65 mmol), Yield 95%). ¹H NMR (300 MHz,CDCl₃) analytical results of the product were as follows:

¹H NMR (300 MHz, CDCl₃):□ [ppm] 1.28(s, 3H), 4.30(t, 2H), 7.20(d, 2H),7.35(d, 1H), 7.73(s, 1H), 7.82(t, 1H), 7.78(d, 1H), 8.22(d, 2H).

Synthesis Example 3 3-(4-nitrophenoxy)benzohydrazide

19 g of ethyl3-(4-nitrophenoxy)benzoate prepared in Synthesis Example 2was dissolved in 200 ml of ethanol, 35 ml of hydrazine monohydrate wasadded thereto, and reacted under reflux for 24 hours. The reactantsolution was poured into excess water and neutralized with 1Nhydrochloric acid, and recrystallized with an ethylacetate solution toyield a product having Formula 27 (15.3 g, Yield 85%). ¹H NMR (300 MHz,CDCl₃) analytical results of the product were as follows:

¹H NMR (300 MHz, CDCl₃):□ [ppm] 1.36 (m, 3H),□4.10 (s, 2H), 7.03 (d,2H), 7.39 (d, 1H), 7.73 (s, 1H), 7.75 (d, 1H), 7.90 (t, 1H), 8.20 (d,2H).

Synthesis Example 4 4-t-butylbenzohydrazide

5.2 g of 4-t-butylbenzoic acid (29.2 mmol) was dissolved in 15 ml ofthionylchloride (206.5 mmol) at room temperature, and a small amount ofN-dimethylformamide (DMF) was added thereto, heated to 80° C. and thenreacted for 8 hours. The crude product was cooled to room temperature,and filtered under reduced pressure for removing thionylchloride, givinga product as a powder, which is then dissolved in 120 ml of THF,followed by adding 35 ml of hydrazine monohydrate (0.722 mol) and 3.7 mlof triethylamine (26.3 mmol) and heating at 65° C. for inducing areaction for 12 hours. After the reaction was completed, filtrationunder reduced pressure was carried out to remove THF and a remainder ofhydrazine monohydrate. Excess water was added to the resultant productand neutralized with hydrochloric acid. After the filtration, thereactant product was recrystallized using ethylacetate to yield aproduct having Formula 28 as a powder (3.5 g, Yield 64%). ¹H NMR (300MHz, CDCl₃) analytical results of the product were as follows:

¹H NMR (300 MHz, CDCl₃):□ [ppm] 1.33 (s, 9H), 4.08-4.11 (m, 3H), 7.44(d, 2H), 7.67 (d, 2H).

Synthesis Example 5 diethyl2,5-bis(hexyloxy)terephthalate

5 g of diethyl-2,5-dihydroxyterephthalate (19.67 mmol) was dissolved in100 ml of dimethylformamide (DMF) at room temperature, 10.87 g ofpotassium carbonate (138.21 mmol) and 16.6 ml of hexylbromide (118.02mmol) were added thereto, and heated to 95° C. for causing a reaction totake place for 12 hours, followed by performing fractional distillationfor removal of DMF and a remainder of hexylbromide. Then, excess waterwas added to the resultant product, neutralized with hydrochloric acid,filtered, and dried under vacuum to yield a product having Formula 29(7.9 g, Yield 95%). ¹H NMR (300 MHz, CDCl₃) analytical results of theproduct were as follows:

¹H NMR (300 MHz, CDCl₃):□ [ppm] 0.92 (s, 6H), 1.39 (m, 16H), 1.43 (m,6H), 4.30 (t, 4H), 4.38 (t, 4H), 7.85 (s, 2H).

Synthesis Example 6 2,5-bis(hexyloxy)terephthalate

7.9 g of diethyl 2,5-dihydroxyterephthalate prepared in SynthesisExample 5 was dissolved in 150 ml of ethanol at room temperature, and asmall amount of potassium hydroxide was added thereto. Then, thereaction mixture was reacted for 12 hours under reflux. The crudeproduct was cooled to room temperature, distilled under reduced pressurefor removing the solvent, followed by adding excess water andhydrochoric acid to adjust the pH level of the reactant solution to pH4. The resultant product was filtered and dried under vacuum to yield5.0 g of a product having Formula 30. ¹H NMR (300 MHz, CDCl₃) analyticalresults of the product were as follows:

¹H NMR (300 MHz, CDCl₃):□ [ppm] 0.92 (d, 6H), 1.34-1.56 (m, 12H), 1.94(m, 4H), 4.30 (t, 4H), 7.88 (s, 2H), 11.14 (s, 2H).

Synthesis Example 7 2,5-bis(hexyloxy)terephthaloxychrloride

1.2 g of 2,5-bis(hexyloxy)terephthalate (3.3 mmol) prepared in SynthesisExample 6 was dissolved in 15 ml of thionylchloride at room temperature,and a small amount of N-dimethylformamide (DMF) was added thereto,heated to 80° C. and then reacted for 6 hours. The crude product wascooled to room temperature, and filtered under reduced pressure forremoving thionylchloride, giving a product having Formula 31 (1.3 g,Yield 98%). ¹H NMR (300 MHz, CDCl₃) analytical results of the productwere as follows:

¹H NMR (300 MHz, CDCl₃):□ [ppm] 0.90 (s, 6H), 1.31-1.49 (m, 12H), 1.83(m, 4H), 4.06 (t, 4H), 7.80 (s, 2H).

Synthesis Example 8N′-1-(4-t-butylbenzoyl)-2,5-bis(hexyloxy)-N′-4-(3-(4-nitrophenoxy)benzoyl)terephthalohydrazide

1.32 g of 2,5-bis(hexyloxy)terephthaloyl dichloride (3.3 mmol) preparedin Synthesis Example 7 was dissolved in 60 ml of THF at roomtemperature, and then added thereto a solution prepared by dissolving0.90 g of 3-(4-nitrophenoxy)benzohydrazide (3.3 mmol) prepared inSynthesis Example 3 and 0.64 g of 4-t-butylbenzohydrazide (3.3 mmol)prepared in Synthesis Example 4 in 30 ml of THF, followed by stirringfor 12 hours for inducing a reaction. After the reaction was completed,the solvent THF was removed at reduced pressure, filtered and performingsilica gel column chromatography (developed with a solution havingethylacetate:n-hexane mixed in a ratio of 1:3) to yield a product havingFormula 32 (1.07 g, Yield 41%). ¹H NMR (300 MHz, CDCl₃) analyticalresults of the product were as follows:

¹H NMR (300 MHz, CDCl₃):□[ppm] 0.88 (m, 9H), 1.25-1.61 (m, 19H), 2.04(m, 4H), 4.25 (t, 4H), 7.00 (d, 2H), 7.48 (d, 2H) 7.53 (d, 1H), 7.66 (s,1H), 7.73 (d, 1H), 7.80-7.84 (m, 3H), 7.88 (s, 1H), 8.19 (d, 2H), 9.57(d, 1H), 9.87 (d, 1H), 11.33 (m, 2H).

Synthesis Example 92-(2,5-bis(hexyloxy)-4-(5-(3-(4-nitrophenoxy)phenyl)-1,3,4-oxadiazole-2-yl)phenyl)-5-(4-t-butylphenyl)-1,3,4-oxadiazole

2.8 g ofN′-1-(4-t-butylbenzoyl)-2,5-bis(hexyloxy)-N′-4-(3-(4-nitrophenoxy)benzoyl)terephthalohydrazide(3.7 mmol) prepared in Synthesis Example 8 was dissolved in 20 ml ofphosphorus oxychloride (POCl₃), heated to 90° C. and then reacted for 12hours. The resultant product was cooled to room temperature, followed byadding excess iced water, neutralizing with sodium hydroxide, filteringand purifying by silica gel column chromatography (developed with asolution having ethylacetate:n-hexane mixed in a ratio of 1:3) to yielda product having Formula 33 (1.1 g, Yield 38%). ¹H NMR (300 MHz, CDCl₃)analytical results of the product were as follows:

¹NMR (300 MHz, CDCl₃):□□[ppm] 0.85 (m, 9H), 1.32-1.42 (m, 18H), 1.91 (m,4H), 4.25 (t, 4H), 7.08 (d, 2H), 7.32 (m, 1H), 7.54-7.66 (m, 2H),7.76-7.91 (m, 3H), 8.02-8.10 (m, 2H), 8.23-8.28 (m, 4H).

Synthesis Example 102-(5-(4-t-butylphenyl)-1,3,4-oxadiazole-2-yl)-5-(5-(3-(4-nitrophenoxy)phenyl)-1,3,4-oxadiazole-2-yl)benzene-1,4-diol

1.1 g of2-(2,5-bis(hexyloxy)-4-(5-(3-(4-nitrophenoxy)phenyl)-1,3,4-oxadiazole-2-yl)phenyl)-5-(4-t-butylphenyl)-1,3,4-oxadiazole(1.44 mmol) prepared in Synthesis Example 9 was dissolved in 60 ml ofdichloromethane at −78° C., and 5 ml of boron tribromide was addedthereto, followed by slowly raising the temperature to 0° C. Thereafter,the reaction was quenched by addition of methanol, followed by addingexcess water. The resultant solution was neutralized withdichloromethane, filtered, and performing silica gel columnchromatography (developed with trichloromethane) to yield a producthaving Formula 34 (0.69 g, Yield 80%). ¹H NMR (300 MHz, CDCl₃)analytical results of the product were as follows:

¹H NMR (300 MHz, CDCl₃): □[ppm] 1.39 (s, 9H), 7.11 (d, 2H), 7.33 (d,1H), 7.58-7.69 (m, 5H), 7.89 (s, 1H), 8.04 (s, 1H), 8.07 (d, 2H), 8.27(d, 2H), 9.79 (s, 1H), 9.91 (s, 1H).

Synthesis Example 112-(5-(3-(4-aminophenoxy)phenyl)-1,3,4-oxadiazole-2-yl)-5-(5-(4-t-butylphenyl)-1,3,4-oxadiazole-2-yl)benzene-1,4-diol

0.69 g of2-(5-(4-t-butylphenyl)-1,3,4-oxadiazole-2-yl)-5-(5-(3-(4-nitrophenoxy)phenyl)-1,3,4-oxadiazole-2-yl)benzene-1,4-diolprepared in Synthesis Example 10 was dissolved in 150 ml of THF, and0.05 g of a catalyst having 5 wt % of palladium impregnated in activatedcarbon was added thereto. Gases generated in the solution by purging anargon (Ar) gas were removed to create a vacuum, followed by stirring for18 hours while supplying H₂ gas (approximately 2-3 atm) for inducing areaction. After the reaction was completed, the reaction product wasfiltered with Celite powder to remove the catalyst, and performingsilica gel column chromatography (developed with a solution havingethylacetate:n-hexane mixed in a ratio of 1:2) to yield a product havingFormula 35 (0.20 g, Yield 30%). ¹H NMR (300 MHz, CDCl₃) analyticalresults of the product were as follows:

¹H NMR (300 MHz, CDCl₃): [ppm] 1.26 (s, 9H), 3.75 (s, 2H), 6.70 (d, 2H),6.90 (d, 2H), 7.08 (d, 1H), 7.42 (t, 1H), 7.53 (d, 2H), 7.72-7.83 (m,4H), 8.06 (d, 2H).

Synthesis Example 122-(5-(4-t-butylphenyl)-1,3,4-oxadiazole-2-yl)-5-(5-(3-(4-(2-(2-hydroxyphenyl)-4,5-diphenyl-1H-imidazole-1-yl)phenoxy)phenyl)-1,3,4-oxadiazole-2-yl)benzene-1,4-diol

0.11 g of benzyl (0.53 mmol) and 0.07 ml of salicylic aldehyde (0.59mmol) were added in 120 ml of iced acetic acid at room temperature, and0.30 g of2-(5-(3-(4-aminophenoxy)phenyl)-1,3,4-oxadiazole-2-yl)-5-(5-(4-t-butylphenyl)-1,3,4-oxadiazole-2-yl)benzene-1,4-diol(0.53 mmol) prepared in Synthesis Example 11 was added thereto, followedby adding 0.41 g of ammonium acetate (5.3 mmol) thereto, heating to 110°C. and reacting for 12 hours. After the reaction was completed, theresultant product was reprecipitated with cyclohexane, recrystallizedwith an ethylacetate solution to yield a product having Formula 22 (0.15g, Yield 32%). ¹H NMR (300 MHz, CDCl₃) analytical results of the productwere as follows:

¹H NMR (300 MHz, CDCl₃):□[ppm] 1.42 (s, 9H), 6.63-6.70 (m, 2H),7.05-7.12 (m, 3H), 7.18-7.36 (m, 12H), 7.56-7.70 (m, 6H), 7.82 (s, 1H),7.95 (d, 1H), 8.10 (d, 2H), 9.86 (s, 1H), 9.5 (s, 1H), 13.39 (s, 2H).

Synthesis Example 132,5-bis(hexyloxy)-N′1,N′4-bis(3-(4-nitrophenoxy)benzoyl)terephthalohydrazide

1.65 g of 2,5-bis(hexyloxy)terephthaloyl dichloride (4.1 mmol) preparedin Synthesis Example 7 was dissolved in 120 ml of THF at roomtemperature, and then added thereto a solution prepared by dissolving2.24 g of 3-(4-nitrophenoxy)benzohydrazide (8.2 mmol) prepared inSynthesis Example 3 in 50 ml of THF, followed by stirring 12 hours forinducing a reaction. After the reaction was completed, THF was removedunder reduced pressure, followed by performing silica gel columnchromatography (developed with a solution having ethylacetate:n-hexanemixed in a ratio of 1:3) to yield a product having Formula 36 (2.7 g,Yield 75%). ¹H NMR (300 MHz, CDCl₃) analytical results of the productwere as follows:

¹H NMR (300 MHz, CDCl₃): □[ppm] 0.88 (t, 6H), 1.33-1.58 (m, 16H), 4.25(t, 4H), 7.03 (d, 4H), 7.30 (d, 2H), 7.55 (d, 2H), 7.65 (s, 2H), 7.71(d, 2H), 7.85 (d, 2H), 8.21 (d, 4H), 9.71 (d, 2H), 11.29 (d, 2H).

Synthesis Example 145,5′-(2,5-bis(hexyloxy)-1,4-phenylene)bis(2-(3-(4-nitrophenoxy)phenyl)-1,3,4-oxadiazole)

2.7 g of2,5-bis(hexyloxy)-N′1,N′4-bis(3-(4-nitrophenoxy)benzoyl)terephthalohydrazide(3.1 mmol) prepared in Synthesis Example 13 was dissolved in 20 ml ofphosphorus oxychloride (POCl₃), heated to 90° C. and then reacted for 12hours. The resultant product was cooled to room temperature, followed byadding excess iced water, neutralizing with sodium hydroxide, filteringand performing silica gel column chromatography (developed with asolution having ethylacetate:n-hexane mixed in a ratio of 1:1) to yielda product having Formula 37 (0.9 g, Yield 30%). ¹H NMR (300 MHz, CDCl₃)analytical results of the product were as follows:

¹H NMR (300 MHz, CDCl₃): [ppm] 0.82-0.91 (m, 6H), 1.25-1.51 (m, 16H),4.16 (m, 4H), 7.05 (d, 4H), 7.31 (d, 2H), 7.61 (t, 2H), 7.83 (s, 2H),7.89 (s, 2H), 8.04 (s, 2H), 8.25 (d, 4H).

Synthesis Example 152,5-bis(5-(3-(4-nitrophenoxy)phenyl)-1,3,4-oxadiazole-2-yl)benzene-1,4-diol

3.04 g of5,5′-(2,5-bis(hexyloxy)-1,4-phenylene)bis(2-(3-(4-nitrophenoxy)phenyl)-1,3,4-oxadiazole)(3.6 mmol) prepared in Synthesis Example 9 was dissolved in 120 ml ofdichloromethane at −78° C., and 3.5 ml of boron tribromide (35.6 mmol)was added thereto, followed by slowly raising the temperature to 0° C.Thereafter, the reaction was quenched by addition of methanol, followedby adding excess water. The resultant solution was neutralized withdichloromethane, filtered, and performing silica gel columnchromatography (developed with trichloromethane) to yield 0.4 g of aproduct having Formula 38. ¹H NMR (300 MHz, CDCl₃) analytical results ofthe product were as follows:

¹H NMR (300 MHz, CDCl₃) □ [ppm] 7.10(d, 4H), 7.34(d, 2H), 7.63(s, 2H),7.69(d, 2H), 7.89(s, 2H), 8.07(d, 2H), 8.26(d, 4H) 12.04 (s, 2H).

Synthesis Example 162,5-bis(5-(3-(4-aminophenoxy)phenyl)-1,3,4-oxadiazole-2-yl)benzene-1,4-diol

0.30 g of2,5-bis(5-(3-(4-nitrophenoxy)phenyl)-1,3,4-oxadiazole-2-yl)benzene-1,4-diolprepared in Synthesis Example 15 was dissolved in 150 ml of THF, and0.05 g of a catalyst having 5 wt % of palladium impregnated in activatedcarbon was added thereto. Gases generated in the solution by purging anargon (Ar) gas were removed to create a vacuum, followed by stirring for18 hours while supplying H₂ gas (approximately 2-3 atm) for inducing areaction. After the reaction was completed, the reaction product wasfiltered with Celite powder to remove the catalyst, and performingsilica gel column chromatography (developed with a solution havingethylacetate:n-hexane mixed in a ratio of 1:2) to yield 0.1 g of aproduct having Formula 39. ¹H NMR (300 MHz, CDCl₃) analytical results ofthe product were as follows:

¹H NMR (300 MHz, CDCl₃) □ [ppm] 4.93(s, 4H), 6.48-7.19(m, 10H),7.34-7.60(m, 4H), 7.68-7.98(m, 6H).

Synthesis Example 172,5-bis(5-(3-(4-(2-(2-hydroxyphenyl)-4,5-diphenyl-1H-imidazole-1-yl)phenoxy)phenyl)-1,3,4-oxadiazole-2-yl)benzene-1,4-diol

0.15 g of benzyl (0.72 mmol) and 0.08 ml of salicylic aldehyde (0.72mmol) were added in 120 ml of iced acetic acid at room temperature, and0.20 g of2,5-bis(5-(3-(4-aminophenoxy)phenyl)-1,3,4-oxadiazole-2-yl)benzene-1,4-diol(0.33 mmol) prepared in Synthesis Example 16 was added thereto, followedby adding 0.50 g of ammonium acetate (6.6 mmol) thereto, heating to 110°C. and reacting for 12 hours. After the reaction was completed, excesswater was added to the resultant product and reprecipitated withcyclohexane, recrystallized with an ethylacetate solution to yield aproduct having Formula 24 (0.012 g, Yield 3.0%). ¹H NMR (300 MHz, CDCl₃)analytical results of the product were as follows:

¹H NMR (300 MHz, CDCl₃) □ [ppm] 6.91(m, 2H), 6.98-7.06(m, 6H),7.10-7.24(m, 20H), 7.32-7.36(m, 2H), 7.41-7.53(m, 8H), 7.74-7.87(m, 8H),12.02-12.10 (m, 4H)

Synthesis Example 18N-(4-(4-(2-(2-hydroxy-phenyl)-4,5-diphenyl-1H-imidazole-1-yl)phenoxy)phenyl)acetamide

4.199 g of benzyl (19.97 mmol) and 2.14 ml of salicylic aldehyde (19.97mmol) were added in 120 ml of iced acetic acid at room temperature, and4.00 g 4,4′-oxydianiline (19.97 mmol) was dropwise added thereto,followed by adding 7.70 g of ammonium acetate (99.8 mmol) thereto,heating to 110° C. and reacting for 12 hours. After the reaction wascompleted, excess water was added to the resultant product andperforming silica gel column chromatography (developed with a solutionhaving ethylacetate:n-hexane mixed in a ratio of 1:3) to yield a producthaving Formula 40 (5.05 g, Yield 47%). ¹H NMR (300 MHz, CDCl₃)analytical results of the product were as follows:

¹H NMR (300 MHz, CDCl₃) □ [ppm] 2.18(s, 3H), 6.53(t, 1H), 6.64(d, 1H),6.92-6.97(m, 4H), 7.06-7.24(m, 10H), 7.28-7.33(m, 3H), 7.48-7.55(m, 4H),13.44(s, 1H).

Synthesis Example 192-(1-(4-(4-aminophenoxy)phenyl)-4,5-diphenyl-1H-imidazole-2-yl)phenol

To 100 ml of a solution prepared by mixing EtOH and water in a volumeratio of 1:1 was added 3.0 g ofN-(4-(4-(2-(2-hydroxyphenyl)-4,5-diphenyl-1H-imidazole-1-yl)phenoxy)phenyl)acetamideprepared in Synthesis Example 18, and 15 ml of hydrochloric acid (37%)was added thereto, and reacted under reflux at 100° C. for 12 hours.After the reaction was completed, excess water was added to theresultant product, and the resultant product was neutralized withpotassium carbonate, filtered, dried and performing silica gel columnchromatography (developed with a solution having ethylacetate:n-hexanemixed in a ratio of 1:3) to yield a product having Formula 41 (2.59 g,Yield 94%). ¹H NMR (300 MHz, CDCl₃) analytical results of the productwere as follows:

¹H NMR (300 MHz, CDCl₃□□□[ppm] 3.73(d,2H), 6.51(t, 1H), 6.64(d, 1H),6.70(d, 2H), 6.83-6.90(m, 4H), 7.05-7.14(m, 3H), 7.15-7.23(m, 6H),7.27-7.31(m, 4H), 7.51(d, 2H)

Synthesis Example 20 3-hydroxy-2 naphthaldehyde(3-hydroxy-2-naphthaldehyde)

4.64 g of 2-naphthol (32.2 mmol) was dissolved in 20 ml of THF, and 43ml of a 1.7 M t-butyltin solution (72.4 mmol) prepared by dissolvingt-butyltin in penthane was dropwise added thereto for 2 minutes. Thegenerated gases were removed and reacted for further 4 hours.Thereafter, the reaction product was cooled to 0° C., and a solutionprepared by adding 12 ml of dimethylformamide to 16 ml of THF was addedthereto and reacted by stirring at room temperature for 24 hours. Anextract was obtained using ethyl acetate and performing silica gelcolumn chromatography (developed with a solution havingethylacetate:n-hexane mixed in a ratio of 1:3) to yield a product havingFormula 42 (0.62 g, Yield 6%). The melting point of the product was100-102° C. and IR(KBr) and ¹H NMR (300 MHz, CDCl₃) analytical resultsof the product were as follows:

IR(KBr) 3390, 3040, 2960, 1665, 1495, 1455, 1380, 1110, 880, 745 cm⁻¹

¹H NMR (300 MHz, CDCl₃):□ [ppm] 7.29 (s, 1H), 7.35 (t, 1H), 7.54 (t,1H), 7.70 (d, 1H), 7.86 (d, 1H), 8.16 (s, 1H), 10.09 (s, 1H), 10.31 (s,1H).

Synthesis Example 213-(1-(4-(4-(2-(2-hydroxyphenyl)-4,5-diphenyl-1H-imidazole-1-yl)phenoxy)phenyl)-4,5-diphenyl-1H-imidazole-2-yl)naphthalene-2-ol

0.30 g of 3-hydroxy-2-naphthaldehyde (1.74 mmol) prepared in SynthesisExample 20 was dissolved in 100 ml of acetic acid, and 0.86 g of2-(1-(4-(4-aminophenoxy)phenyl)-4,5-diphenyl-1H-imidazole-2-yl)phenol(1.74 mmol) prepared in Synthesis Example 19, 0.37 g of benzyl (1.74mmol) and 0.94 g of ammonium acetate (12.2 mmol) were added thereto,followed by heating to 110° C. and reacting for 12 hours. Thereafter,excess water was added to the resultant product and performing silicagel column chromatography (developed with a solution havingethylacetate:n-hexane mixed in a ratio of 1:3) to yield a product havingFormula 18 (0.67 g, Yield 45%). ¹H NMR (300 MHz, CDCl₃) and ¹³C NMR (500MHz, CDCl₃) analytical results of the product were as follows:

¹H NMR (300 MHz, CDCl₃):□ [ppm] 6.48 (t, 1H), 6.62 (d, 1H), 6.96-7.02(m, 4H), 7.10-7.24 (m, 13H), 7.27-7.42 (m, 11H), 7.52-7.66 (m, 6H),13.09 (s, 1H), 13.36 (s, 1H).

¹³C NMR (500 MHz, CDCl₃): [ppm] 110.05, 111.45, 113.75, 116.38, 116.44,118.06, 118.54, 121.71, 124.39, 124.53, 125.20, 125.29, 125.42, 125.50,125.64, 125.78, 126.42, 126.84, 126.89, 127.09, 127.16, 128.17, 128.32,128.60, 128.89, 128.98, 129.89, 131.38, 131.47, 133.18, 134.54, 143.05,143.56, 153.78, 153.32, 157.02.

Example 1

A film was formed on a glass substrate by doping 6 wt % of the compound(W1) of Formula 22 prepared in Synthesis Example 12, the compound (W2)of Formula 24 prepared in Synthesis Example 17, and the compound (W3) ofFormula 18 prepared in Synthesis Example 21. Photoluminescence (PL)spectral analysis was performed on the film, and the PL analyticalresult is shown in FIG. 4 and the CIE color coordinate is shown in FIG.6. The PL analysis was performed using a 325 nm He—Cd laser as a lightsource and a GaAs detector with quantum efficiency in the 300-900-nmspectral range as a photodetector.

To compare the PL analytical results of the white-emitting monomolecularcompounds according to the present invention and the conventional ESIPTmolecules, 2-(1,4,5-triphenyl-1H-imidazole-2-yl)phenol (HPI, λ_(max)=460nm), 5-bis(5-(4-tert-butylphenyl)-1,3,4-oxadiazole-2-yl)benzene-1,4-diol(DOX, λ_(max)=580 nm) and3-(1,4,5-triphenyl-1H-imidazole-2-yl)naphthalene-2-ol(HPNI, λ_(max)=580nm) were doped to be contained in polystylene each in an amount of 6 wt%, forming films. The PL spectral analysis was performed on the films.The PL analytical results for the conventional ESIPT molecules, that is,HPI, HPNI and DOX, are shown in FIG. 5 and the CIE color coordinatesthereof are shown in FIG. 6.

As shown in FIG. 4, the compounds W1, W2, and W3 synthesized accordingto the present invention showed absorbance peaks at 347, 320, and 330nm. As shown in FIG. 6, based on the color coordinate (0.33, 0.33), asindicated by symbol Δ, showing ideal white luminescence, the colorcoordinates of the compounds W1, W2 and W3, as indicated by symbols ◯,□, and ⋄, were (0.45, 0.40), (0.28, 0.29), and (0.33, 0.37),respectively, confirming efficient white luminescence. This ispresumably because the white-emitting monomolecular compounds accordingto the present invention prepared by covalently bonding two or moreESIPT molecules developing different colors could prevent the energytransfer by completely restricting an interaction between an energyacceptor and an energy donor.

Example 2

To confirm luminescence intensity depending on changes in theconcentrations of the white-emitting monomolecular compounds accordingto the present invention, for example, the compound W3, was added toCHCl₃ while varying its concentrations, that is, 1×10⁻³M, 1×10⁻⁴M and1×10⁻⁵M, and PL spectral analysis was performed thereon. The PL spectralanalysis results are shown in FIG. 7.

As confirmed from FIG. 7, the PL intensity of the white-emittingmonomolecular compound according to the present invention, that is, thecompound W3, could be adjusted by varying its concentration.

Example 3

Each of the conventional ESIPT molecules HPI, W3 and HPNI was added toCHCl₃ in a concentration 1×10⁻⁵M, and then thinly dispersed on a glasssubstrate, followed by UV lamp irradiation using a 365 nm UV lamp. TheUV lamp irradiation results are shown in FIG. 8.

As confirmed from FIG. 8, the white-emitting monomolecular compoundaccording to the present invention, that is, the compound W3, showedefficient white luminescence.

Example 4

A film was formed on a glass substrate by doping 6 wt % of the compoundW3 having Formula 18 prepared in Synthesis Example 21 into polystylene.The film was exposed to absorption intensity of 347 nm, and normalizedPL intensities were measured over time at 450 nm and 690 nm,respectively. The measurement results are shown in FIGS. 9 and 10.

To compare the PL intensity of the compound W3 with that of theconventional ESIPT monomolecule, a film was formed by doping 6 wt % ofeach of HPI and HPNI into polystylene. Each film was exposed toabsorption intensity of 347 nm, and the normalized PL intensities forHPI and HPNI were measured over time at 450 nm and 690 nm, respectively.The measurement results are shown in FIGS. 11 and 12.

As shown in FIGS. 9 through 12, the white-emitting monomolecularcompound according to the present invention, that is, the compound W3,exhibited substantially the same PL intensity with HPI and HPNI.

Experimental Example 1 Fabrication and Evaluation of White OrganicElectroluminescent Element

A glass substrate having a 25 mm×25 mm×1.1 mm indium tin oxide (ITO)transparent electrode was subjected to ultrasonic cleaning for 5minutes, followed by UV ozone cleaning for 30 minutes. The cleaned glasssubstrate having the transparent electrode was mounted on a substrateholder of a vacuum deposition device, and4,4′-bis[N-(1-naphthyl)-N-phenyl-amino]-biphenyl (NPD) as a holetransport material was deposited on a surface of the glass substratehaving the transparent electrode to a thickness of 40 nm, forming afilm, and the compound W3 of Formula 18 prepared in Synthesis Example 21was formed thereon to a thickness of 30 nm. Thereafter,4,7-diphenyl-1,10-phenantroline (Bphen) as an electron transportingmaterial was formed into a film having a thickness of 50 nm, and an Lilayer was formed thereon to a thickness 1 nm at a rate of 0.1 Å/sec,followed by depositing Al on the Li film to form an electrode having athickness of 100 nm, thereby fabricating an organic electroluminescentelement. During deposition, deposition equipment (Sunicel plus 200)manufactured by Sunic System Ltd. of Korea was used.

The efficiency of the fabricated OLED was measured using a PhotoResearch PR650 spectrometer, and the I-V characteristic of thefabricated OLED was measured using a Keithley 236 source measure unit.The measurement results are shown in Table 1 and the wavelengthdependent PL intensity is shown in FIG. 13.

TABLE 1 Driving Luminance Efficiency Color (at 10 mA/cm²) voltage [V][cd/m²] [cd/A] coordinates Experimental 9.71 97 0.97 0.343, 0.291Example 1

As confirmed from Table 1 and FIG. 13, when the white-emittingmonomolecular compound according to the present invention is applied toan OLED, efficient white luminescence can be achieved.

Experimental Example 2 Application of the Inventive Compound to a LaserDevice

The compound W3 having Formula 18 prepared in Synthesis Example 21 wasallowed to grow in ethylacetate into single crystals, and pulse-excitedemission spectra were measured using an actively/passively mode-locked355 nm Nd:YAG Laser (Quantel, YG701). By optically pumping, amplifiedspontaneous emission (ASE), also known as mirrorless lasing, wasobserved, and the results are shown in FIG. 14. Here, Spectrapro-500manufactured by Acton Research Corp. was used to observe the ASE.

Although exemplary embodiments of the present invention have beendescribed in detail hereinabove, it should be understood that manyvariations and modifications of the basic inventive concept hereindescribed, which may appear to those skilled in the art, will still fallwithin the spirit and scope of the exemplary embodiments of the presentinvention as defined by the appended claims.

What is claimed is:
 1. A white-emitting monomolecular compound represented by Formula 21:

wherein R₄ is selected from the group consisting of a hydrogen atom, a hydroxy group, a linear, branched or cyclic C1-C20 alkyl group, a C1-C20 alkoxy group, a substituted or unsubstituted C1-C20 carbonyl group, an aryloxy group substituted with an aromatic or cyclic compound, a halogen atom, a trifluoromethyl group, a C1-C20 sulfonic group substituted with an alkyl group, a sulfonic group substituted with an aromatic cyclic compound or an aryl group, a C1-C20 substituted alkylamide group, an arylamide group substituted with an aromatic cyclic compound or an aryl group, an amino group, a nitro group, and a cyano group; R₂ and R₃ are each independently selected from the group consisting of a hydrogen atom, a hydroxy group, a linear, branched or cyclic C1-C20 alkyl group, a C1-C20 alkoxy group, a substituted or unsubstituted C1-C20 carbonyl group, an aryloxy groupsubstituted with an aromatic or cyclic compound, a halogen atom, a trifluoromethyl group, a C1-C20 sulfonic group substituted with an alkylgroup, a sulfonic group substituted with an aromatic cyclic compound or an aryl group, a C1-C20 substituted alkylamide group, an arylamide group substituted with an aromatic cyclic compound or an aryl group, an amino group, a nitro group, a cyano group, a sulfone amide group, a thiol group, and a fluorous acid group, which contain hydrogen capable of forming a hydrogen bond with a nitrogen atom of an adjacent ring; and R₁ is selected from the group consisting of a hydroxyl group, an amino group, an alkylamide group, an arylamide group, a sulfone amide group, a sulfonic group substituted with an aromatic cyclic compound or an aryl group, a thiol group, and a fluorous acid group, which contain hydrogen capable of forming a hydrogen bond with a nitrogen atom of an adjacent ring.
 2. The white-emitting monomolecular compound of claim 1, wherein the white-emitting monomolecular compound of claim 1 is represented by Formula 22:


3. An organic electroluminescent element comprising the white-emitting monomolecular compound of claim
 1. 4. A laser device including the white-emitting monomolecular compound of claim
 1. 5. The organic electroluminescent element of claim 3, wherein the white-emitting monomolecular compound of claim 1 is represented by Formula
 22. 6. The laser device of claim 4, wherein the white-emitting monomolecular compound of claim 1 is represented by Formula
 22. 